1. Field of the Invention
This invention relates to a TAB (tape automated bonding) tape with a stiffener as radiation and reinforcement plate, a method of making the same, and a tape BGA (ball grid array) semiconductor device using the TAB tape.
2. Description of the Related Art
Tape BGA semiconductor devices are used for sever control of communication device etc. The tape BGA semiconductor device is required to operate at a high-frequency region of tens of GHz according to increase in transmission speed. Thus, it needs characteristics such as high radiation and low noise. Because of this, the tape substrate used is a double-sided wiring tape where ground potential layer and signal wiring layer are separated, and a stiffener of copper alloy etc. with a good radiation performance is adhered to the tape through adhesive.
FIG. 1 shows a conventional tape BGA semiconductor device. The tape BGA semiconductor device is composed of: an insulating tape 5 of, e.g., polyimide with flexibility; a first wiring pattern 10 that is formed on the surface of insulating tape 5; a second wiring pattern 11 that is formed on the back surface of insulating tape 5; via holes 6 that are provided in the insulating tape 5 to allow electrical conduction between the first and second wiring patterns 10, 11, a stiffener 8 that is adhered under the insulating tape 5 through adhesive 7; a semiconductor chip 1 that is mounted on the stiffener 8 in a cavity 15; bonding wires 9 that connect between electrodes (not shown) of the semiconductor chip 1 and terminals (not shown) of the first wiring pattern 10; and solder balls 3 that are connected with the first wiring pattern 10 and are used as electrodes to connect with an external circuit (not shown).
The semiconductor chip 1 and the bonding wires 9 are sealed with sealing resin 2. PSR (photosensitive solder resist) layer 4 is formed on the first wiring pattern 10 side, except regions that the solder balls 3 are mounted and the sealing resin 2 is provided, to prevent a deviation in shape of solder ball or a short circuit between solder balls when mounting the solder balls.
The first wiring pattern 10 is used mainly as signal layer, and the second wiring pattern 11 is, as described later, composed of ground potential layer and leads.
A method of making the above tape BGA semiconductor device will be described below.
FIGS. 2A to 2K show a process of making the conventional tape BGA semiconductor device with stiffener. FIGS. 3A to 3C show a process of making the stiffener 8 in FIG. 1.
At first, a copper-covered substrate is prepared that first and second copper foils 10a and 11a are adhered to both surfaces of insulating tape 5 of polyimide film etc. (FIG. 2A). Then, through-holes 6a are formed by punching (FIG. 2B). Both surfaces of the copper-covered substrate with through-holes 6a are copper-plated (FIG. 2C). Via hole 6 is formed that copper-plated layer 6b allows electrical conduction between the first copper foil 10a and the second copper foil 11a, and first and second copper-plated layers 10b and 11b are formed on the first and second copper foils 10a and 11a. 
Then, photoresist 14 with a predetermined pattern is coated (FIG. 2D). By conducting the exposure and development, portions where no wiring pattern is to be formed in the first and second copper-plated layer 10b, 11b are exposed (FIG. 2E). The exposed first and second copper-plated layer 10b, 11b and the exposed first and second copper foils 10a, 11a are removed by etching to form the first and second wiring patterns 10, 11 (FIG. 2F). At that time, leads 30, 31 and ground potential layer 21 are also formed in the second wiring pattern 11.
Photoresist 14 is removed (FIG. 2G). On a suitable place of the first copper foil 10a side, PSR 4 is coated that prevents a deviation in shape of solder ball or a short circuit between solder balls when mounting the solder balls (FIG. 2H).
Then, adhesive 7 is coated on the second wiring pattern 11 side (FIG. 2I). A cavity 15 is formed that houses the semiconductor chip (FIG. 2J). The stiffener 8 is adhered to the back surface of the insulating tape 5 (FIG. 2K). Then, by thermally curing the adhesive 7, the TAB tape with stiffener is obtained.
The stiffener 8 is prepared as follows. A copper plate 12 (FIG. 3A) is shaped to have a given pattern by pressing or punching (FIG. 3B). Then, it is subject to blackening treatment 13 so as to enhance the adhesiveness with adhesive 7 (FIG. 3C).
The semiconductor chip 1 is mounted on the stiffener 8 of TAB tape thus obtained on the cavity 15 side. Electrodes (not shown) of the semiconductor chip 1 is connected through the bonding wires 9 with the first wiring pattern 10. Then, the semiconductor chip 1 and bonding wires 9 are sealed with sealing resin 2.
By mounting solder balls 3 at a predetermined position of the first wiring pattern 10, the tape BGA semiconductor device is obtained (FIG. 1).
However, in the conventional TAB tape with stiffener, as shown in FIGS. 4A and 4B, void 16 may occur in the surface where the stiffener 8 is adhered through adhesive 7 since the adhesive 7 is not necessarily enough provided into parts 32, 33 and 34 where no lead is formed in the second wiring pattern 11 or the adhesive itself includes air bubble. Because of this, there is a problem that there may occur peeling of copper layer of the leads 30, 31 in second wiring pattern 11 from the stiffener 8 and migration thereof due to expansion of void in the reflow of solder ball.